<p>
  测试view钩子,父组件调用子组件方法
</p>
<!--父类中声明@ViewChild变量-->
<app-view-child #child1></app-view-child>
<app-view-child #child2></app-view-child>
<button type="button" (click)="child2.greeting('Jerry')">调用Chlids方法</button>
